from __future__ import annotations

import contextlib
import logging
import random
import struct
import uuid
from collections.abc import AsyncIterable, AsyncIterator, Iterable, Mapping
from types import TracebackType
from typing import Any, Literal, overload

import trio
import trio.abc

from ..asyncio.compatibility import (
    TimeoutError,
    aiter,
    anext,
)
from ..exceptions import (
    ConcurrencyError,
    ConnectionClosed,
    ConnectionClosedOK,
    ProtocolError,
)
from ..frames import DATA_OPCODES, CloseCode, Frame, Opcode
from ..http11 import Request, Response
from ..protocol import CLOSED, OPEN, Event, Protocol, State
from ..typing import BytesLike, Data, DataLike, LoggerLike, Subprotocol
from .messages import Assembler


__all__ = ["Connection"]


class Connection(trio.abc.AsyncResource):
    """
    :mod:`trio` implementation of a WebSocket connection.

    :class:`Connection` provides APIs shared between WebSocket servers and
    clients.

    You shouldn't use it directly. Instead, use
    :class:`~websockets.trio.client.ClientConnection` or
    :class:`~websockets.trio.server.ServerConnection`.

    """

    def __init__(
        self,
        nursery: trio.Nursery,
        stream: trio.abc.Stream,
        protocol: Protocol,
        *,
        ping_interval: float | None = 20,
        ping_timeout: float | None = 20,
        close_timeout: float | None = 10,
        max_queue: int | None | tuple[int | None, int | None] = 16,
    ) -> None:
        self.nursery = nursery
        self.stream = stream
        self.protocol = protocol
        self.ping_interval = ping_interval
        self.ping_timeout = ping_timeout
        self.close_timeout = close_timeout
        if isinstance(max_queue, int) or max_queue is None:
            max_queue_high, max_queue_low = max_queue, None
        else:
            max_queue_high, max_queue_low = max_queue

        # Inject reference to this instance in the protocol's logger.
        self.protocol.logger = logging.LoggerAdapter(
            self.protocol.logger,
            {"websocket": self},
        )

        # Copy attributes from the protocol for convenience.
        self.id: uuid.UUID = self.protocol.id
        """Unique identifier of the connection. Useful in logs."""
        self.logger: LoggerLike = self.protocol.logger
        """Logger for this connection."""
        self.debug = self.protocol.debug

        # HTTP handshake request and response.
        self.request: Request | None = None
        """Opening handshake request."""
        self.response: Response | None = None
        """Opening handshake response."""

        # Lock stopping reads when the assembler buffer is full.
        self.recv_flow_control = trio.Lock()

        # Assembler turning frames into messages and serializing reads.
        self.recv_messages = Assembler(
            max_queue_high,
            max_queue_low,
            pause=self.recv_flow_control.acquire_nowait,
            resume=self.recv_flow_control.release,
        )

        # Deadline for the closing handshake.
        self.close_deadline: float | None = None

        # Lock preventing concurrent calls to send_all or send_eof.
        self.send_lock = trio.Lock()

        # Protect sending fragmented messages.
        self.send_in_progress: trio.Event | None = None

        # Mapping of ping IDs to pong waiters, in chronological order.
        self.pending_pings: dict[bytes, tuple[trio.Event, float, bool]] = {}

        self.latency: float = 0.0
        """
        Latency of the connection, in seconds.

        Latency is defined as the round-trip time of the connection. It is
        measured by sending a Ping frame and waiting for a matching Pong frame.
        Before the first measurement, :attr:`latency` is ``0``.

        By default, websockets enables a :ref:`keepalive <keepalive>` mechanism
        that sends Ping frames automatically at regular intervals. You can also
        send Ping frames and measure latency with :meth:`ping`.
        """

        # Exception raised while reading from the connection, to be chained to
        # ConnectionClosed in order to show why the TCP connection dropped.
        self.recv_exc: BaseException | None = None

        # Completed when the TCP connection is closed and the WebSocket
        # connection state becomes CLOSED.
        self.stream_closed: trio.Event = trio.Event()

        # Start recv_events only after all attributes are initialized.
        self.nursery.start_soon(self.recv_events)

    # Public attributes

    @property
    def local_address(self) -> Any:
        """
        Local address of the connection.

        For IPv4 connections, this is a ``(host, port)`` tuple.

        The format of the address depends on the address family.
        See :meth:`~socket.socket.getsockname`.

        """
        if isinstance(self.stream, trio.SSLStream):  # pragma: no cover
            stream = self.stream.transport_stream
        else:
            stream = self.stream
        if isinstance(stream, trio.SocketStream):
            return stream.socket.getsockname()
        else:  # pragma: no cover
            raise NotImplementedError(f"unsupported stream type: {stream}")

    @property
    def remote_address(self) -> Any:
        """
        Remote address of the connection.

        For IPv4 connections, this is a ``(host, port)`` tuple.

        The format of the address depends on the address family.
        See :meth:`~socket.socket.getpeername`.

        """
        if isinstance(self.stream, trio.SSLStream):  # pragma: no cover
            stream = self.stream.transport_stream
        else:
            stream = self.stream
        if isinstance(stream, trio.SocketStream):
            return stream.socket.getpeername()
        else:  # pragma: no cover
            raise NotImplementedError(f"unsupported stream type: {stream}")

    @property
    def state(self) -> State:
        """
        State of the WebSocket connection, defined in :rfc:`6455`.

        This attribute is provided for completeness. Typical applications
        shouldn't check its value. Instead, they should call :meth:`~recv` or
        :meth:`send` and handle :exc:`~websockets.exceptions.ConnectionClosed`
        exceptions.

        """
        return self.protocol.state

    @property
    def subprotocol(self) -> Subprotocol | None:
        """
        Subprotocol negotiated during the opening handshake.

        :obj:`None` if no subprotocol was negotiated.

        """
        return self.protocol.subprotocol

    @property
    def close_code(self) -> int | None:
        """
        State of the WebSocket connection, defined in :rfc:`6455`.

        This attribute is provided for completeness. Typical applications
        shouldn't check its value. Instead, they should inspect attributes
        of :exc:`~websockets.exceptions.ConnectionClosed` exceptions.

        """
        return self.protocol.close_code

    @property
    def close_reason(self) -> str | None:
        """
        State of the WebSocket connection, defined in :rfc:`6455`.

        This attribute is provided for completeness. Typical applications
        shouldn't check its value. Instead, they should inspect attributes
        of :exc:`~websockets.exceptions.ConnectionClosed` exceptions.

        """
        return self.protocol.close_reason

    # Public methods

    async def __aenter__(self) -> Connection:
        return self

    async def __aexit__(
        self,
        exc_type: type[BaseException] | None,
        exc_value: BaseException | None,
        traceback: TracebackType | None,
    ) -> None:
        if exc_type is None:
            await self.aclose()
        else:
            await self.aclose(CloseCode.INTERNAL_ERROR)

    async def __aiter__(self) -> AsyncIterator[Data]:
        """
        Iterate on incoming messages.

        The iterator calls :meth:`recv` and yields messages asynchronously in an
        infinite loop.

        It exits when the connection is closed normally. It raises a
        :exc:`~websockets.exceptions.ConnectionClosedError` exception after a
        protocol error or a network failure.

        """
        try:
            while True:
                yield await self.recv()
        except ConnectionClosedOK:
            return

    @overload
    async def recv(self, decode: Literal[True]) -> str: ...

    @overload
    async def recv(self, decode: Literal[False]) -> bytes: ...

    @overload
    async def recv(self, decode: bool | None = None) -> Data: ...

    async def recv(self, decode: bool | None = None) -> Data:
        """
        Receive the next message.

        When the connection is closed, :meth:`recv` raises
        :exc:`~websockets.exceptions.ConnectionClosed`. Specifically, it raises
        :exc:`~websockets.exceptions.ConnectionClosedOK` after a normal closure
        and :exc:`~websockets.exceptions.ConnectionClosedError` after a protocol
        error or a network failure. This is how you detect the end of the
        message stream.

        Canceling :meth:`recv` is safe. There's no risk of losing data. The next
        invocation of :meth:`recv` will return the next message.

        This makes it possible to enforce a timeout by wrapping :meth:`recv` in
        :func:`~trio.move_on_after` or :func:`~trio.fail_after`.

        When the message is fragmented, :meth:`recv` waits until all fragments
        are received, reassembles them, and returns the whole message.

        Args:
            decode: Set this flag to override the default behavior of returning
                :class:`str` or :class:`bytes`. See below for details.

        Returns:
            A string (:class:`str`) for a Text_ frame or a bytestring
            (:class:`bytes`) for a Binary_ frame.

            .. _Text: https://datatracker.ietf.org/doc/html/rfc6455#section-5.6
            .. _Binary: https://datatracker.ietf.org/doc/html/rfc6455#section-5.6

            You may override this behavior with the ``decode`` argument:

            * Set ``decode=False`` to disable UTF-8 decoding of Text_ frames and
              return a bytestring (:class:`bytes`). This improves performance
              when decoding isn't needed, for example if the message contains
              JSON and you're using a JSON library that expects a bytestring.
            * Set ``decode=True`` to force UTF-8 decoding of Binary_ frames
              and return a string (:class:`str`). This may be useful for
              servers that send binary frames instead of text frames.

        Raises:
            ConnectionClosed: When the connection is closed.
            ConcurrencyError: If two coroutines call :meth:`recv` or
                :meth:`recv_streaming` concurrently.

        """
        try:
            return await self.recv_messages.get(decode)
        except EOFError:
            pass
            # fallthrough
        except ConcurrencyError:
            raise ConcurrencyError(
                "cannot call recv while another coroutine "
                "is already running recv or recv_streaming"
            ) from None
        except UnicodeDecodeError as exc:
            async with self.send_context():
                self.protocol.fail(
                    CloseCode.INVALID_DATA,
                    f"{exc.reason} at position {exc.start}",
                )
            # fallthrough

        # Wait for the protocol state to be CLOSED before accessing close_exc.
        await self.stream_closed.wait()
        raise self.protocol.close_exc from self.recv_exc

    @overload
    def recv_streaming(self, decode: Literal[True]) -> AsyncIterator[str]: ...

    @overload
    def recv_streaming(self, decode: Literal[False]) -> AsyncIterator[bytes]: ...

    @overload
    def recv_streaming(self, decode: bool | None = None) -> AsyncIterator[Data]: ...

    async def recv_streaming(self, decode: bool | None = None) -> AsyncIterator[Data]:
        """
        Receive the next message frame by frame.

        This method is designed for receiving fragmented messages. It returns an
        asynchronous iterator that yields each fragment as it is received. This
        iterator must be fully consumed. Else, future calls to :meth:`recv` or
        :meth:`recv_streaming` will raise
        :exc:`~websockets.exceptions.ConcurrencyError`, making the connection
        unusable.

        :meth:`recv_streaming` raises the same exceptions as :meth:`recv`.

        Canceling :meth:`recv_streaming` before receiving the first frame is
        safe. Canceling it after receiving one or more frames leaves the
        iterator in a partially consumed state, making the connection unusable.
        Instead, you should close the connection with :meth:`aclose`.

        Args:
            decode: Set this flag to override the default behavior of returning
                :class:`str` or :class:`bytes`. See below for details.

        Returns:
            An iterator of strings (:class:`str`) for a Text_ frame or
            bytestrings (:class:`bytes`) for a Binary_ frame.

            .. _Text: https://datatracker.ietf.org/doc/html/rfc6455#section-5.6
            .. _Binary: https://datatracker.ietf.org/doc/html/rfc6455#section-5.6

            You may override this behavior with the ``decode`` argument:

            * Set ``decode=False`` to disable UTF-8 decoding of Text_ frames
              and return bytestrings (:class:`bytes`). This may be useful to
              optimize performance when decoding isn't needed.
            * Set ``decode=True`` to force UTF-8 decoding of Binary_ frames
              and return strings (:class:`str`). This is useful for servers
              that send binary frames instead of text frames.

        Raises:
            ConnectionClosed: When the connection is closed.
            ConcurrencyError: If two coroutines call :meth:`recv` or
                :meth:`recv_streaming` concurrently.

        """
        try:
            async for frame in self.recv_messages.get_iter(decode):
                yield frame
            return
        except EOFError:
            pass
            # fallthrough
        except ConcurrencyError:
            raise ConcurrencyError(
                "cannot call recv_streaming while another coroutine "
                "is already running recv or recv_streaming"
            ) from None
        except UnicodeDecodeError as exc:
            async with self.send_context():
                self.protocol.fail(
                    CloseCode.INVALID_DATA,
                    f"{exc.reason} at position {exc.start}",
                )
            # fallthrough

        # Wait for the protocol state to be CLOSED before accessing close_exc.
        await self.stream_closed.wait()
        raise self.protocol.close_exc from self.recv_exc

    async def send(
        self,
        message: DataLike | Iterable[DataLike] | AsyncIterable[DataLike],
        text: bool | None = None,
    ) -> None:
        """
        Send a message.

        A string (:class:`str`) is sent as a Text_ frame. A bytestring or
        bytes-like object (:class:`bytes`, :class:`bytearray`, or
        :class:`memoryview`) is sent as a Binary_ frame.

        .. _Text: https://datatracker.ietf.org/doc/html/rfc6455#section-5.6
        .. _Binary: https://datatracker.ietf.org/doc/html/rfc6455#section-5.6

        You may override this behavior with the ``text`` argument:

        * Set ``text=True`` to send an UTF-8 bytestring or bytes-like object
          (:class:`bytes`, :class:`bytearray`, or :class:`memoryview`) in a
          Text_ frame. This improves performance when the message is already
          UTF-8 encoded, for example if the message contains JSON and you're
          using a JSON library that produces a bytestring.
        * Set ``text=False`` to send a string (:class:`str`) in a Binary_
          frame. This may be useful for servers that expect binary frames
          instead of text frames.

        :meth:`send` also accepts an iterable or asynchronous iterable of
        strings, bytestrings, or bytes-like objects to enable fragmentation_.
        Each item is treated as a message fragment and sent in its own frame.
        All items must be of the same type, or else :meth:`send` will raise a
        :exc:`TypeError` and the connection will be closed.

        .. _fragmentation: https://datatracker.ietf.org/doc/html/rfc6455#section-5.4

        :meth:`send` rejects dict-like objects because this is often an error.
        (If you really want to send the keys of a dict-like object as fragments,
        call its :meth:`~dict.keys` method and pass the result to :meth:`send`.)

        Canceling :meth:`send` is discouraged. Instead, you should close the
        connection with :meth:`aclose`. Indeed, there are only two situations
        where :meth:`send` may yield control to the event loop and then get
        canceled; in both cases, :meth:`aclose` has the same effect and is
        more clear:

        1. The write buffer is full. If you don't want to wait until enough
           data is sent, your only alternative is to close the connection.
           :meth:`aclose` will likely time out then abort the TCP connection.
        2. ``message`` is an asynchronous iterator that yields control.
           Stopping in the middle of a fragmented message will cause a
           protocol error and the connection will be closed.

        When the connection is closed, :meth:`send` raises
        :exc:`~websockets.exceptions.ConnectionClosed`. Specifically, it
        raises :exc:`~websockets.exceptions.ConnectionClosedOK` after a normal
        connection closure and
        :exc:`~websockets.exceptions.ConnectionClosedError` after a protocol
        error or a network failure.

        Args:
            message: Message to send.

        Raises:
            ConnectionClosed: When the connection is closed.
            TypeError: If ``message`` doesn't have a supported type.

        """
        # While sending a fragmented message, prevent sending other messages
        # until all fragments are sent.
        while self.send_in_progress is not None:
            await self.send_in_progress.wait()

        # Unfragmented message -- this case must be handled first because
        # strings and bytes-like objects are iterable.

        if isinstance(message, str):
            async with self.send_context():
                if text is False:
                    self.protocol.send_binary(message.encode())
                else:
                    self.protocol.send_text(message.encode())

        elif isinstance(message, BytesLike):
            async with self.send_context():
                if text is True:
                    self.protocol.send_text(message)
                else:
                    self.protocol.send_binary(message)

        # Catch a common mistake -- passing a dict to send().

        elif isinstance(message, Mapping):
            raise TypeError("data is a dict-like object")

        # Fragmented message -- regular iterator.

        elif isinstance(message, Iterable):
            chunks = iter(message)
            try:
                chunk = next(chunks)
            except StopIteration:
                return

            assert self.send_in_progress is None
            self.send_in_progress = trio.Event()
            try:
                # First fragment.
                if isinstance(chunk, str):
                    async with self.send_context():
                        if text is False:
                            self.protocol.send_binary(chunk.encode(), fin=False)
                        else:
                            self.protocol.send_text(chunk.encode(), fin=False)
                    encode = True
                elif isinstance(chunk, BytesLike):
                    async with self.send_context():
                        if text is True:
                            self.protocol.send_text(chunk, fin=False)
                        else:
                            self.protocol.send_binary(chunk, fin=False)
                    encode = False
                else:
                    raise TypeError("iterable must contain bytes or str")

                # Other fragments
                for chunk in chunks:
                    if isinstance(chunk, str) and encode:
                        async with self.send_context():
                            self.protocol.send_continuation(chunk.encode(), fin=False)
                    elif isinstance(chunk, BytesLike) and not encode:
                        async with self.send_context():
                            self.protocol.send_continuation(chunk, fin=False)
                    else:
                        raise TypeError("iterable must contain uniform types")

                # Final fragment.
                async with self.send_context():
                    self.protocol.send_continuation(b"", fin=True)

            except Exception:
                # We're half-way through a fragmented message and we can't
                # complete it. This makes the connection unusable.
                async with self.send_context():
                    self.protocol.fail(
                        CloseCode.INTERNAL_ERROR,
                        "error in fragmented message",
                    )
                raise

            finally:
                self.send_in_progress.set()
                self.send_in_progress = None

        # Fragmented message -- async iterator.

        elif isinstance(message, AsyncIterable):
            achunks = aiter(message)
            try:
                chunk = await anext(achunks)
            except StopAsyncIteration:
                return

            assert self.send_in_progress is None
            self.send_in_progress = trio.Event()
            try:
                # First fragment.
                if isinstance(chunk, str):
                    if text is False:
                        async with self.send_context():
                            self.protocol.send_binary(chunk.encode(), fin=False)
                    else:
                        async with self.send_context():
                            self.protocol.send_text(chunk.encode(), fin=False)
                    encode = True
                elif isinstance(chunk, BytesLike):
                    if text is True:
                        async with self.send_context():
                            self.protocol.send_text(chunk, fin=False)
                    else:
                        async with self.send_context():
                            self.protocol.send_binary(chunk, fin=False)
                    encode = False
                else:
                    raise TypeError("async iterable must contain bytes or str")

                # Other fragments
                async for chunk in achunks:
                    if isinstance(chunk, str) and encode:
                        async with self.send_context():
                            self.protocol.send_continuation(chunk.encode(), fin=False)
                    elif isinstance(chunk, BytesLike) and not encode:
                        async with self.send_context():
                            self.protocol.send_continuation(chunk, fin=False)
                    else:
                        raise TypeError("async iterable must contain uniform types")

                # Final fragment.
                async with self.send_context():
                    self.protocol.send_continuation(b"", fin=True)

            except Exception:
                # We're half-way through a fragmented message and we can't
                # complete it. This makes the connection unusable.
                async with self.send_context():
                    self.protocol.fail(
                        CloseCode.INTERNAL_ERROR,
                        "error in fragmented message",
                    )
                raise

            finally:
                self.send_in_progress.set()
                self.send_in_progress = None

        else:
            raise TypeError("data must be str, bytes, iterable, or async iterable")

    async def aclose(
        self,
        code: CloseCode | int = CloseCode.NORMAL_CLOSURE,
        reason: str = "",
    ) -> None:
        """
        Perform the closing handshake.

        :meth:`aclose` waits for the other end to complete the handshake and
        for the TCP connection to terminate.

        :meth:`aclose` is idempotent: it doesn't do anything once the
        connection is closed.

        Args:
            code: WebSocket close code.
            reason: WebSocket close reason.

        """
        try:
            # The context manager takes care of waiting for the TCP connection
            # to terminate after calling a method that sends a close frame.
            async with self.send_context():
                if self.send_in_progress is not None:
                    self.protocol.fail(
                        CloseCode.INTERNAL_ERROR,
                        "close during fragmented message",
                    )
                else:
                    self.protocol.send_close(code, reason)
        except ConnectionClosed:
            # Ignore ConnectionClosed exceptions raised from send_context().
            # They mean that the connection is closed, which was the goal.
            pass
        # Safety net: enforce the semantics of trio.abc.AsyncResource.aclose().
        except BaseException:  # pragma: no cover
            await trio.aclose_forcefully(self.stream)

    async def wait_closed(self) -> None:
        """
        Wait until the connection is closed.

        :meth:`wait_closed` waits for the closing handshake to complete and for
        the TCP connection to terminate.

        """
        await self.stream_closed.wait()

    async def ping(
        self,
        data: DataLike | None = None,
        ack_on_close: bool = False,
    ) -> trio.Event:
        """
        Send a Ping_.

        .. _Ping: https://datatracker.ietf.org/doc/html/rfc6455#section-5.5.2

        A ping may serve as a keepalive or as a check that the remote endpoint
        received all messages up to this point

        Args:
            data: Payload of the ping. A :class:`str` will be encoded to UTF-8.
                If ``data`` is :obj:`None`, the payload is four random bytes.
            ack_on_close: when this option is :obj:`True`, the event will also
                be set when the connection is closed. While this avoids getting
                stuck waiting for a pong that will never arrive, it requires
                checking that the state of the connection is still ``OPEN`` to
                confirm that a pong was received, rather than the connection
                being closed.

        Returns:
            An event that will be set when the corresponding pong is received.
            You can ignore it if you don't intend to wait.

            ::

                pong_received = await ws.ping()
                # only if you want to wait for the corresponding pong
                await pong_received.wait()

        Raises:
            ConnectionClosed: When the connection is closed.
            ConcurrencyError: If another ping was sent with the same data and
                the corresponding pong wasn't received yet.

        """
        if isinstance(data, BytesLike):
            data = bytes(data)
        elif isinstance(data, str):
            data = data.encode()
        elif data is not None:
            raise TypeError("data must be str or bytes-like")

        async with self.send_context():
            # Protect against duplicates if a payload is explicitly set.
            if data in self.pending_pings:
                raise ConcurrencyError("already waiting for a pong with the same data")

            # Generate a unique random payload otherwise.
            while data is None or data in self.pending_pings:
                data = struct.pack("!I", random.getrandbits(32))

            pong_received = trio.Event()
            ping_timestamp = trio.current_time()
            self.pending_pings[data] = (pong_received, ping_timestamp, ack_on_close)
            self.protocol.send_ping(data)
            return pong_received

    async def pong(self, data: DataLike = b"") -> None:
        """
        Send a Pong_.

        .. _Pong: https://datatracker.ietf.org/doc/html/rfc6455#section-5.5.3

        An unsolicited pong may serve as a unidirectional heartbeat.

        Args:
            data: Payload of the pong. A :class:`str` will be encoded to UTF-8.

        Raises:
            ConnectionClosed: When the connection is closed.

        """
        if isinstance(data, BytesLike):
            data = bytes(data)
        elif isinstance(data, str):
            data = data.encode()
        else:
            raise TypeError("data must be str or bytes-like")

        async with self.send_context():
            self.protocol.send_pong(data)

    # Private methods

    def process_event(self, event: Event) -> None:
        """
        Process one incoming event.

        This method is overridden in subclasses to handle the handshake.

        """
        assert isinstance(event, Frame)
        if event.opcode in DATA_OPCODES:
            self.recv_messages.put(event)

        if event.opcode is Opcode.PONG:
            self.acknowledge_pings(bytes(event.data))

    def acknowledge_pings(self, data: bytes) -> None:
        """
        Acknowledge pings when receiving a pong.

        """
        # Ignore unsolicited pong.
        if data not in self.pending_pings:
            return

        pong_timestamp = trio.current_time()

        # Sending a pong for only the most recent ping is legal.
        # Acknowledge all previous pings too in that case.
        ping_id = None
        ping_ids = []
        for ping_id, (
            pong_received,
            ping_timestamp,
            _ack_on_close,
        ) in self.pending_pings.items():
            ping_ids.append(ping_id)
            pong_received.set()
            if ping_id == data:
                self.latency = pong_timestamp - ping_timestamp
                break
        else:
            raise AssertionError("solicited pong not found in pings")

        # Remove acknowledged pings from self.pending_pings.
        for ping_id in ping_ids:
            del self.pending_pings[ping_id]

    def acknowledge_pending_pings(self) -> None:
        """
        Acknowledge pending pings when the connection is closed.

        """
        assert self.protocol.state is CLOSED

        for pong_received, _ping_timestamp, ack_on_close in self.pending_pings.values():
            if ack_on_close:
                pong_received.set()

        self.pending_pings.clear()

    async def keepalive(self) -> None:
        """
        Send a Ping frame and wait for a Pong frame at regular intervals.

        """
        assert self.ping_interval is not None
        try:
            while True:
                # If self.ping_timeout > self.latency > self.ping_interval,
                # pings will be sent immediately after receiving pongs.
                # The period will be longer than self.ping_interval.
                with trio.move_on_after(self.ping_interval - self.latency):
                    await self.stream_closed.wait()
                    break

                try:
                    pong_received = await self.ping(ack_on_close=True)
                except ConnectionClosed:
                    break
                if self.debug:
                    self.logger.debug("% sent keepalive ping")

                if self.ping_timeout is not None:
                    with trio.move_on_after(self.ping_timeout) as cancel_scope:
                        await pong_received.wait()
                        if self.debug:
                            self.logger.debug("% received keepalive pong")
                    if cancel_scope.cancelled_caught:
                        if self.debug:
                            self.logger.debug("- timed out waiting for keepalive pong")
                        async with self.send_context():
                            self.protocol.fail(
                                CloseCode.INTERNAL_ERROR,
                                "keepalive ping timeout",
                            )
                        break
        except Exception:
            self.logger.error("keepalive ping failed", exc_info=True)

    def start_keepalive(self) -> None:
        """
        Run :meth:`keepalive` in a task, unless keepalive is disabled.

        """
        if self.ping_interval is not None:
            self.nursery.start_soon(self.keepalive)

    async def recv_events(self) -> None:
        """
        Read incoming data from the stream and process events.

        Run this method in a task as long as the connection is alive.

        ``recv_events()`` exits immediately when ``self.stream`` is closed.

        """
        try:
            while True:
                try:
                    # If the assembler buffer is full, block until it drains.
                    async with self.recv_flow_control:
                        pass
                    data = await self.stream.receive_some()
                except Exception as exc:
                    if self.debug:
                        self.logger.debug(
                            "! error while receiving data",
                            exc_info=True,
                        )
                    # When the closing handshake is initiated by our side,
                    # recv() may block until send_context() closes the stream.
                    # In that case, send_context() already set recv_exc.
                    # Calling set_recv_exc() avoids overwriting it.
                    self.set_recv_exc(exc)
                    break

                if data == b"":
                    break

                # Feed incoming data to the protocol.
                self.protocol.receive_data(data)

                # This isn't expected to raise an exception.
                events = self.protocol.events_received()

                # Write outgoing data to the stream.
                try:
                    await self.send_data()
                except Exception as exc:
                    if self.debug:
                        self.logger.debug(
                            "! error while sending data",
                            exc_info=True,
                        )
                    # Similarly to the above, avoid overriding an exception
                    # set by send_context(), in case of a race condition
                    # i.e. send_context() closes the transport after recv()
                    # returns above but before send_data() calls send().
                    self.set_recv_exc(exc)
                    break

                # If needed, set the close deadline based on the close timeout.
                if self.protocol.close_expected():
                    if self.close_deadline is None and self.close_timeout is not None:
                        self.close_deadline = trio.current_time() + self.close_timeout

                # If self.send_data raised an exception, then events are lost.
                # Given that automatic responses write small amounts of data,
                # this should be uncommon, so we don't handle the edge case.

                for event in events:
                    # This isn't expected to raise an exception.
                    self.process_event(event)

            # Breaking out of the while True: ... loop means that we believe
            # that the stream doesn't work anymore.

            # Feed the end of the data stream to the protocol.
            self.protocol.receive_eof()

            # This isn't expected to raise an exception.
            events = self.protocol.events_received()

            # There is no error handling because send_data() can only write
            # the end of the data stream here and it handles errors itself.
            await self.send_data()

            # This code path is triggered when receiving an HTTP response
            # without a Content-Length header. This is the only case where
            # reading until EOF generates an event; all other events have
            # a known length. Ignore for coverage measurement because tests
            # are in test_client.py rather than test_connection.py.
            for event in events:  # pragma: no cover
                # This isn't expected to raise an exception.
                self.process_event(event)

        except Exception as exc:
            # This branch should never run. It's a safety net in case of bugs.
            self.logger.error("unexpected internal error", exc_info=True)
            self.set_recv_exc(exc)
        finally:
            # This isn't expected to raise an exception.
            await self.close_stream()

    @contextlib.asynccontextmanager
    async def send_context(
        self,
        *,
        expected_state: State = OPEN,  # CONNECTING during the opening handshake
    ) -> AsyncIterator[None]:
        """
        Create a context for writing to the connection from user code.

        On entry, :meth:`send_context` checks that the connection is open; on
        exit, it writes outgoing data to the socket::

            async with self.send_context():
                self.protocol.send_text(message.encode())

        When the connection isn't open on entry, when the connection is expected
        to close on exit, or when an unexpected error happens, terminating the
        connection, :meth:`send_context` waits until the connection is closed
        then raises :exc:`~websockets.exceptions.ConnectionClosed`.

        """
        # Should we wait until the connection is closed?
        wait_for_close = False
        # Should we close the stream and raise ConnectionClosed?
        raise_close_exc = False
        # What exception should we chain ConnectionClosed to?
        original_exc: BaseException | None = None

        if self.protocol.state is expected_state:
            # Let the caller interact with the protocol.
            try:
                yield
            except (ProtocolError, ConcurrencyError):
                # The protocol state wasn't changed. Exit immediately.
                raise
            except Exception as exc:
                self.logger.error("unexpected internal error", exc_info=True)
                # This branch should never run. It's a safety net in case of
                # bugs. Since we don't know what happened, we will close the
                # connection and raise the exception to the caller.
                wait_for_close = False
                raise_close_exc = True
                original_exc = exc
            else:
                # Check if the connection is expected to close soon.
                if self.protocol.close_expected():
                    wait_for_close = True
                    # Set the close deadline based on the close timeout.
                    # Since we tested earlier that protocol.state is OPEN
                    # (or CONNECTING), self.close_deadline is still None.
                    assert self.close_deadline is None
                    if self.close_timeout is not None:
                        self.close_deadline = trio.current_time() + self.close_timeout
                # Write outgoing data to the socket with flow control.
                try:
                    await self.send_data()
                except Exception as exc:
                    if self.debug:
                        self.logger.debug("! error while sending data", exc_info=True)
                    # While the only expected exception here is OSError,
                    # other exceptions would be treated identically.
                    wait_for_close = False
                    raise_close_exc = True
                    original_exc = exc

        else:  # self.protocol.state is not expected_state
            # Minor layering violation: we assume that the connection
            # will be closing soon if it isn't in the expected state.
            wait_for_close = True
            # Calculate close_deadline if it wasn't set yet.
            if self.close_deadline is None and self.close_timeout is not None:
                self.close_deadline = trio.current_time() + self.close_timeout
            raise_close_exc = True

        # If the connection is expected to close soon and the close timeout
        # elapses, close the socket to terminate the connection.
        if wait_for_close:
            if self.close_deadline is not None:
                with trio.move_on_at(self.close_deadline) as cancel_scope:
                    await self.stream_closed.wait()
                if cancel_scope.cancelled_caught:
                    # There's no risk to overwrite another error because
                    # original_exc is never set when wait_for_close is True.
                    assert original_exc is None
                    original_exc = TimeoutError("timed out while closing connection")
                    # Set recv_exc before closing the transport in order to get
                    # proper exception reporting.
                    raise_close_exc = True
                    self.set_recv_exc(original_exc)
            else:
                await self.stream_closed.wait()

        # If an error occurred, close the transport to terminate the connection and
        # raise an exception.
        if raise_close_exc:
            await self.close_stream()
            raise self.protocol.close_exc from original_exc

    async def send_data(self) -> None:
        """
        Send outgoing data.

        """
        # Serialize calls to send_all().
        async with self.send_lock:
            for data in self.protocol.data_to_send():
                if data:
                    await self.stream.send_all(data)
                else:
                    # Half-close the TCP connection when possible i.e. no TLS.
                    if isinstance(self.stream, trio.abc.HalfCloseableStream):
                        if self.debug:
                            self.logger.debug("x half-closing TCP connection")
                        try:
                            await self.stream.send_eof()
                        except Exception:  # pragma: no cover
                            pass
                    # Else, close the TCP connection.
                    else:  # pragma: no cover
                        if self.debug:
                            self.logger.debug("x closing TCP connection")
                        await self.stream.aclose()

    def set_recv_exc(self, exc: BaseException | None) -> None:
        """
        Set recv_exc, if not set yet.

        """
        if self.recv_exc is None:
            self.recv_exc = exc

    async def close_stream(self) -> None:
        """
        Shutdown and close stream. Close message assembler.

        Calling close_stream() guarantees that recv_events() terminates. Indeed,
        recv_events() may block only on stream.recv() or on recv_messages.put().

        """
        # Close the stream.
        await self.stream.aclose()

        # Calling protocol.receive_eof() is safe because it's idempotent.
        # This guarantees that the protocol state becomes CLOSED.
        self.protocol.receive_eof()
        assert self.protocol.state is CLOSED

        # Abort recv() with a ConnectionClosed exception.
        self.recv_messages.close()

        # Acknowledge pings sent with the ack_on_close option.
        self.acknowledge_pending_pings()

        # Unblock coroutines waiting on self.stream_closed.
        self.stream_closed.set()
